Urinary stones that form as a consequence of urinary infection account for approximately 20 percent of all urinary stones. The morbidity and mortality that result from infection-induced stones is considerably higher than all other forms of urinary stones. Clinical reports from many centers over the past fifty years have strongly implicated urea-splitting bacteria as the primary causative agent for infection-induced stones. Recent experimental investigations from this laboratory have noted that the urease enzyme is the primary and perhaps the sole mechanism involved in the pathogenesis of infection-induced stones. Acetohydroxamic Acid (AHA) which is manufactured in our laboratory (IND#10149) is an effective inhibitor of the bacterial enzyme urease. Experimental studies (in vitro and in vivo) have shown that AHA in pharmacological doses will successfully prevent the formation of infection-induced urinary stones. Clinical studies have been initiated with AHA in patients with renal calculi and associated urea-splitting bacterial infection. Twenty three patients have taken AHA for periods varying from six to eighteen months. The drug has been well tolerated at a dose of 1.0 gm per day. Urinary ammonia and pH have been reduced in every patient receiving the drug. Stone growth and stone recurrence has not occurred in any patient receiving the drug. Data has not yet evolved regarding the question as to whether urease inhibition may result in clinical dissolution of renal stones. A reversible hemolytic anemia has occurred in three patients. This side effect was dose related and completely reversible. These three patients are now taking AHA at reduced levels. It is believed that AHA may be an effective form of chemotherapeutic agent in patients with persistent, chronic, and/or recurrent urea-splitting urinary infection in whom stone growth and/or stone recurrence is a problem. BIBLIOGRAPHIC REFERENCES: Griffith, D.P., Itin, C., Tyler, M., and Musher, D.M.: Urease: The primary cause of infection-induced urinary stones. Invest. Urol. 13:346-350, 1976. Griffith, D.P., Bragin, S. and Musher, D.M.: Dissolution of struvite urinary stones: Experimental studies in vitro. Invest. Urol. 13:351-353, 1976.